1. LHC results on open heavy quarks and quarkonia 1 E. Scomparin (INFN-Torino) Heavy quarks and quarkonia in thermal QCD Trento, 2-5 April 2013

2. A new episode of a long story…. 2 …27 years after the prediction of J/ suppression by Matsui and Satz … 17 years after the prediction of radiative energy loss by the BDMPS group

3. A new episode of a long story…. 3 …27 years after O beams were first accelerated in the SPS …13 years after Au beams were first accelerated at RHIC … and barely 2.5 years (!!!) after Pb beams first circulated inside the LHC

4. Are LHC results matching our expectations? 4 Definitely yes !

5. ..and RHIC is keeping pace 5 …but we will focus today on LHC

6. Heavy quark energy loss… 6  Fundamental test of our understanding of the energy loss mechanism, since E depends on  Properties of the medium  Path length..but should critically depend on the properties of the parton  Casimir factor  Quark mass (dead cone effect) E quark < E gluon E b < E c < E light q which should imply R AA (B) > R AA (D) > R AA () S. Wicks, M. Gyulassy, JPG35 (2008) 054001

7. … and v 2  Due to their large mass, c and b quarks should take longer time (= more re-scatterings) to be influenced by the collective expansion of the medium  v 2 (b) < v 2 (c)  Uniqueness of heavy quarks: cannot be destroyed and/or created in the medium  Transported through the full system evolution 7 Can the unprecedented abundance of heavy quarks produced at the LHC bring to a (final ?) clarification of the picture ? J. Uphoff et al., PLB 717 (2012), 430

8. LHC, 3 factories for heavy quark in Pb-Pb 8 ALICE ATLAS CMS

9. A (slightly) closer look to experiments: CMS 9  “Global” muons reconstructed with information from inner tracker and muon stations  Further muon ID based on track quality (χ2, # hits,…)  Magnetic field and material limit minimum momentum for muon detection  p T cut for J/  Tracker p T resolution: 1-2% up to p T ~100 GeV/c  Separation of quarkonium states  Displaced tracks for heavy-flavour measurements

10. A (slightly) closer look to experiments: ALICE 10  Main difference with respect to CMS: PID over a large p T range, down to low p T (~0.1 GeV/c)  TPC as main tracker  slower detector, lower luminosity  “Intermediate” situation for the forward muon arm  Faster detectors, can stand higher luminosity

11. “Indirect” measurements  Semileptonic decays, the shortcut to heavy quark production (pioneered by RHIC and also SPS!)  ALICE: HF muons at forward rapidity (-4<<-2.5)  Non-negligible background issues

12. Results Forward muon spectrometer  Background from /K extrapolated from mid-y (assuming y-dep. of R AA )  Factor ~3-4 suppression for central events, weak p T - dependence  Reference: pp at 2.76 TeV  Muon ID: matching track/trigger, rejects hadronic punch-through 0-10% 10-20% 20-40% 40-60% 60-80%

13. What about central rapidity ? 13  ATLAS measures muons from HF in ||<1.05, 4<p T <14 GeV/c  No pp at 2.76 TeV reference available, use R CP rather than R AA  R CP subject to statistical fluctuations  use R PC too!  ~flat vs p T up to 14 GeV/c, different from inclusive R CP ! HF yield through fit of templates for discriminant variable C If ~no suppression for 60-80%  central ~ forward suppression

14. Electron ID in ALICE 14  Low-p T electrons identified mainly via dE/dx in the TPC for MB events  High-p T electrons: EMCal becomes essential (in addition to TPC)  Check matching of the distributions in the common p T region

15. Electrons at midrapidity 15  ALICE measures inclusive electron production at midrapidity  “Photonic” background subtraction through invariant mass reconstruction (pair candidate with other e and reject low masses)  Contribution from J/  ee also subtracted Suppression in 3<p T <18 GeV/c (factor up to ~3) Hints for less suppession at high p T ? Reference: pp at 7 Tev + FONLL

16. Reconstructing D-decay topology 16  ALICE: good vertexing resolution + PID  study D-decay topology  Topology of the decay resolved via the reconstruction of secondary vertex  Combinatorial background reduced via topological selections (e.g. cos point )  PID using TOF and TPC to further suppress background  Invariant mass analysis c ~ 300 m c ~ 120 m

17. More complex topologies 17  D*: look for soft pion from primary vertex (strong decay)  100-200 MeV momentum, detection in the ITS (no PID)  Small Q-value, signal at the beginning of m plot, background not too large  D s : small c factor wrt D +  2K PID helps removing background, but not enough  Selection around -mass

18. D-meson R AA 18  ALICE: D-mesons at central rapidity  Invariant mass analysis of fully reconstructed decay topologies displaced from the primary vertex  D 0, D + and D* + R AA agree within uncertainties Strong suppression of prompt D mesons in central collisions  up to a factor of 5 for p T ≈ 10 GeV/c  Reference  7 TeV scaled to 2.76 with FONLL  Use FONLL shape if no pp

19. Comparisons: what do we learn? 19  To properly compare D and leptons the decay kinematics should be considered (p T e ≈0.5·p T B at high p T e )  Similar trend vs. p T for D, charged particles and  ± Hint of R AA D > R AA π at low p T ?  Look at beauty

20. Charm(ed) and strange: D S R AA 20  First measurement of D s + in AA collisions  Expectation: enhancement of the strange/non-strange D meson yield at intermediate p T if charm hadronizes via recombination in the medium  Strong D s + suppression (similar as D 0, D + and D* + ) for 8<p T <12 GeV/c  R AA seems to increase at low p T  Current data do not allow a conclusive comparison to other D mesons within uncertainties

21. Beauty via displaced J/ 21  Fraction of non-prompt J/ from simultaneous fit to  +  - invariant mass spectrum and pseudo-proper decay length distributions  (pioneered by CDF)  Background from sideways (sum of 3 exp.)  Signal and prompt from MC template

22. Non-prompt J/ 22 Suppression hierarchy (b vs c) observed, at least for central collisions (note different y range) Larger suppression at high p T ? (Slightly) larger forward suppression

23. The new frontier: b-jet tagging 23  Jets are tagged by cutting on discriminating variables based on the flight distance of the secondary vertex  enrich the sample with b-jets  b-quark contribution extracted using template fits to secondary vertex invariant mass distributions Factor 100 light-jet rejection for 45% b-jet efficiency

24. b-jet vs centrality/p T 24  b-fraction ~constant vs both p T and centrality  b-fraction similar (within errors) in p-p and Pb-Pb Pb-Pb/pp

25. Beauty vs light: high vs low p T 25  Low p T : different suppression for beauty and light flavours, but:  Different centrality  Decay kinematics  High p T : similar suppression for light flavour and b-tagged jets Fill the gap!

26. HQ v 2 at the LHC 26 Indication of non-zero D meson v 2 (3 effect) in 2<p T <6 GeV/c  First direct measurement of D anisotropy in heavy-ion collisions  Yield extracted from invariant mass spectra of K candidates in 2 bins of azimuthal angle relative to the event plane

27. EP dependence of R AA (30-50%) 27  Raw yield in and out of plane in 30-50%  Efficiencies from MC simulations  Feed-down subtraction with FONLL  Reference: 7TeV pp data scaled to 2.76 TeV More suppression out of plane with respect to in plane: longer path length at high p T, elliptic flow at low p T

28. Electron v 2 28  As for single-electron R AA, different detection techniques according to p T  Magnitude of v 2 comparable at RHIC/LHC in the common p T range  HFE v 2 >0 observed in 20-40% >3 in 2<p T <3 GeV/c  Suggests strong re-interaction with the medium

29. Data vs models: D-mesons 29 Consistent description of charm R AA and v 2 very challenging for models, can bring insight on the medium transport properties, also with more precise data from future LHC runs

30. Data vs models: HFE 30 Simultaneous description of heavy-flavor electrons R AA and v 2 Challenge for theoretical models

31. Heavy quark – where are we ?  Abundant heavy flavour production at the LHC  Allow for precision measurements  Can separate charm and beauty (vertex detectors!)  Indication for R AA beauty >R AA charm and R AA beauty >R AA light  More statistics needed to conclude on R AA charm vs. R AA light  Indication (3) for non-zero charm elliptic flow at low p T  Hadrochemistry of D meson species:first intriguing result on D s

32. Intermezzo: multiplicity dependence of D and J/ yields 32  Should help to explore the role of multi-parton interactions in pp collisions  The ~linear increase of the yields with charged multiplicities and the similar behaviour for D and J/ are remarkable….. …but need to be explained!

33. Charmonia – the legacy 33  The first “hard probe” to be extensively studied  Several years of investigation at SPS and RHIC energies After correction for EKS98 shadowing In-In 158 GeV (NA60) Pb-Pb 158 GeV (NA50) PHENIX  Suppression beyond cold nuclear matter effects (firmly) established  Role of (re)generation still under debate Still producing new results !

34. Great expectations for LHC 34 …along two main lines 1) Evidence for charmonia (re)combination: now or never! Yes, we can!   (3S)  b (2P)  (2S)  b (1P)  (1S) 2) A detailed study of bottomonium suppression  Finally a clean probe, as J/ at SPS

35. Once again, the main actors 35 Will LHCb join the club ? CMS J/: |y| 6.5 GeV/c ALICE J/: |y|<0.9,2.5<y<4 p T >0 ATLAS |  | 3 GeV/c Complementary kinematic coverage!

36. ALICE, focus on low-p T J/ 36  Electron analysis: background subtracted with event mixing  Signal extraction by event counting |y|<0.9  Muon analysis: fit to the invariant mass spectra  signal extraction by integrating the Crystal Ball line shape

37. J/, ALICE vs PHENIX 37  Compare with PHENIX  Stronger centrality dependence at lower energy  Systematically larger R AA values for central events in ALICE Is this the expected signature for (re)combination ?  Even at the LHC, NO rise of J/ yield for central events, but….

38. R AA vs N part  in p T bins  In the models, ~50% of low-p T J/ are produced via (re)combination, while at high p T the contribution is negligible  fair agreement from N part ~100 onwards  J/ production via (re)combination should be more important at low transverse momentum  Different suppression pattern for low- and high- p T J/  Smaller R AA for high p T J/  Compare R AA vs N part  for low-p T (0<p T <2 GeV/c) and high-p T (5<p T <8 GeV/c) J/ recombination 38

39. R AA vs p T 39  Expect smaller suppression for low-p T J/  observed! The trend is different wrt the one observed at lower energies, where an increase of the with centrality was obtained  Fair agreement with transport models and statistical model

40. CMS, focus on high p T  Muons need to overcome the magnetic field and energy loss in the absorber  Minimum total momentum p~3-5 GeV/c to reach the muon stations  Limits J/ acceptance  Midrapidity: p T >6.5 GeV/c  Forward rapidity: p T >3 GeV/c..but not the  one (p T > 0 everywhere)

41. CMS explores the high p T region 41  (Maybe) we still see a hint of p T dependence of the suppression even in the p T range explored by CMS  Good agreement with ALICE in spite of the different rapidity range (which anyway seems not to play a major role at high p T ) Centrality dep. in pTpT y bins

42. CMS vs STAR high-p T suppression 42  (Re)combination effects should be negligible  CMS: prompt J/ p T > 6.5 GeV/c, |y|<2.4 0-5%  factor 5 suppression 60-100%  factor 1.4 suppression  STAR: inclusive J/ p T >5 GeV/c, |y|<1 High p T : less suppression at RHIC than at LHC

43. Rapidity dependence 43  Rather pronounced in ALICE, and evident in the forward region (~40% decrease in R AA in 2.5<y<4)  More difficult to conclude between mid- and forward-rapidity  Not so pronounced at high p T (see CMS, previous slides)  PHENIX-like ?? Shadowing estimate (EPS09, nDSg) Compatible with central, NOT with forward y More general CNM issue

44. Does the J/ finally flow ? 44  First hint for J/ flow in heavy-ion collisions (ALICE, forward y) !  The contribution of J/ from (re)combination should lead to a significant elliptic flow signal at LHC energy  Significance up to 3.5  for chosen kinematic/centrality selections  Qualitative agreement with transport models including regeneration

45. J/ at the LHC: a “summary” plot 45  Main “qualitative” features now explored  Effect of “inclusive” (ALICE) vs “prompt” (CMS) expected to be small  Precise theory calculations are now needed! “Onset” of regeneration at small y, p T ?

46. J/ and open charm, more questions 46  Is the apparent similarity of D and J/ R AA telling us something ?  In principle suppression mechanisms are different (en. loss vs suppression) but….

47. (2S): CMS vs ALICE 47  (2S) much less bound than J/  Results from the SPS showed a larger suppression than for J/ (saturating towards central events ? One of the landmarks of stat. model)  No results from RHIC in Au-Au  Seen by both CMS (much better resolution!) and ALICE, different kinem. Expectations for LHC ?

48. Enhancement/suppression ? 48  At SPS, the suppression increased with centrality (the opposite for CMS)  Overall interpretation is challenging  ALICE vs CMS: should we worry? Probably not, seen the size of the errors  Large uncertainties: signal extraction, pp reference  Work needed to reduce systematics  CMS: transition from strong (relative) enhancement to suppression in a relatively narrow p T range ALICE excludes a large enhancement

49. Finally, the  49  LHC is really the machine for studying bottomonium in AA collisions (and CMS the best suited experiment to do that!)

50. Strong suppression of (2S), wrt to (1S)  Separated ϒ (2S) and ϒ (3S)  Measured ϒ (2S)/ ϒ (1S)double ratio vs. centrality  centrality integrated  no strong centrality dependence  Upper limit on ϒ (3S)  centrality integrated One of the long-awaited signatures ?

51. First accurate determination of  suppression 51  Suppression increases with centrality  First determination of (2S) R AA : already suppressed in peripheral collisions  (1S) compatible with only feed-down suppression ?  Probably yes, also taking into account the normalization uncertainty Compatible with STAR (but large uncorrelated errors): expected ? Is (1S) dissoc. threshold still beyond LHC reach ?  Full energy

52. What did we learn ? 52  26 years after first suppression prediction, this is observed also in the bottomonium sector with a very good accuracy  R AA vs binding energy qualitatively interesting: can different p T coverage be seen as a way to “kill” recombination ?

53. Quarkonia – where are we ? 53  Two main mechanisms at play 1)Suppression in a deconfined medium 2)Re-generation (for charmonium only!) at high s can qualitatively explain the main features of the results  ALICE is fully exploiting the physics potential in the charmonium sector (optimal coverage at low p T and reaching 8-10 GeV/c)  R AA  weak centrality dependence at all y, larger than at RHIC  Less suppression at low p T with respect to high p T  CMS is fully exploiting the physics potential in the bottomonium sector (excellent resolution, all p T coverage)  Clear ordering of the suppression of the three  states with their binding energy  as expected from sequential melting  (1S) suppression consistent with excited state suppression (50% feed-down)

54. CNM: will pA help ? 54  In principle, yes !  In practice, it is often difficult to  Understand the results  Use them to calculate CNM for AA SPS RHIC  We might be a bit more lucky at LHC since shadowing might become the only CNM effect  Crossing times ~10 -3 fm/c  Much smaller than formation times

55. News from pA run 55 Goal: 30 nb -1 integrated luminosity  reached Data taken for p-Pb AND Pb-p: maximum forward rapidity coverage p-Pb peak luminosity > 10 29 cm -2 s -1 ALICE Asymmetric energy of the two beams s=5.023 TeV y=0.465

56. A taste of what’s coming 56 Calibrate CNM effects  within reach for both HF and quarkonia!

57. Conclusions 57 LHC: first round of observations EXTREMELY fruitful  Many (most) of the heavy-quark/quarkonia related observables were investigated, no showstoppers, first physics extracted  Many (most) of the heavy-quark/quarkonia related observables need more data to sharpen the conclusions  full energy run, 2015-2017  upgrades, 2018 onwards RHIC: still a main actor, with upgraded detectors Lower energies: SPS, FAIR  Serious experimental challenge  High- B region of the phase diagram unexplored for what concerns heavy quark/quarkonia below 158 GeV/c

58. Recent news from RHIC 58  STAR: direct charm measurement vs p T, in bins of centrality  pp reference consistent with FONLL upper limit Suppression at high-p T in central and mid-central collisions Enhancement at “intermediate” p T (consistent with resonance re-combination model) J. Bielcik

59. PHENIX, b vs c 59 PHENIX VTX tracker Larger suppression for beauty  Challenging result ! TO BE UNDERSTOOD  Charm to bottom ratio is obtained from the fit to the DCA distribution of measured electrons  Good agreement with previous NPE results and with pp b/c ratios R. Akimoto TO BE BETTER UNDERSTOOD !

60. PHENIX, b vs c 60  Charm and bottom contributions in electron from heavy-quark decay is measured directly from the electron DCA distribution (VTX)  Bottom fraction in pp consistent with published data (from e-h correlations ) and with FONLL Look forward to forthcoming Au-Au results! R. Akimoto

61. STAR, on R AA and v 2 61  1 nb -1 sampled luminosity (Run2010)  new measurement of NPE with a highly improved result at high p T  v 2 tends to zero at low s  lighter charm-medium interactions ?  Strong suppression of HQ (consistent with D), pure energy loss disfavoured  Finite v 2 at low p T, increase at high p T (jet corr., path length dependence)  Simultaneous description of R AA and v 2  challenge for models M. Mustafa

62. PHENIX – new systems/energies 62  Old system (Au-Au) at new energy: still a balancing of suppression and regeneration ?  Theory seems to say so….  New system (Cu-Au) at old energy: Cu-going finally different! (probably not a CNM effect)  A challenge to theory  SPS went the other way round (from S-U to Pb-Pb…) M. Durham

63. PHENIX – CNM 63  First study of a charmonium excited state at collider energy  Seems contradicting our previous knowledge  p T dependence of R dAu  Increase vs p T at central/forward y  Reminds SPS observation  But different behaviour at backward rapidity  Not easy to reproduce in models! Overall picture still not clear !

64. STAR – J/ 64  STAR measures high-p T J/ up to 10 GeV/c  Fair agreement with models including color screening and recombination (the latter becomes negligible at low p T )  First measurement of J/ v 2 (will become final ?)  Compatible with zero everywhere  In contrast with recombination picture ? B. Trzeciak

65. STAR -  65  Bottomonium: the “clean” probe  3 states with very different binding energies  No complications from recombination But not that easy at RHIC! …and this has been split into 3 centrality bins…. Compatible with 3S melting and 2S partial melting M. Calderon

66. Hints from theory 66  Theory is on the data ! Fair agreement, but….  … one model has no CNM, no regeneration  …the other one has both CNM and regeneration Still too early to claim a satisfactory understanding ?